1. Field of the Invention
The present invention relates to a radio button telephone system in which a parent telephone set and a child telephone set are connected by radio waves.
2. Description of the Related Art
A radio button telephone system is composed of a parent telephone set and a plurality of child telephone sets. The construction of the conventional radio button telephone system will now be explained in reference to FIGS. 1A and 1B.
FIG. 1A is a diagram showing the construction of a parent telephone set of the conventional radio button telephone system, and FIG. 1B is a diagram showing the construction of a child telephone set thereof. In FIG. 1A, reference numeral 1 denotes a line controller for outputting line seizure, disconnect, and select signals to a line connected to the parent telephone set and ensuring a voice signal channel. Numeral 2 denotes a bell detector for detecting a bell signal generated on the line at the time of call incoming. The line controller 1 and the bell detector 2 form a city telephone interface section 6.
Numeral 3 denotes a communication controller for making the communication of control data and a voice signal with a child telephone set or a private radio button telephone set. A plurality of communication controllers 3 may be prepared to cope with a plurality of child telephone sets. Numeral 4 denotes a channel switch for connecting and releasing a voice channel between any public telephone interface section 6 and any communication controller 3. Numeral 5 denotes an exchange controller for detecting a physical change in extension telephone and public telephone lines from the bell detector 2 and the communication controller 3 to control the line controller 1 and the channel switch 4 in accordance with a change in condition.
In FIG. 1B, reference numeral 7 denotes a child telephone set, numeral 8 a line condition display lamp for displaying the condition of a line connected to the public telephone interface section 6 such as a condition in which the line is in use, a condition in which the line is under call incoming and so forth, and numeral 9 an operation button such as a dial for operating the telephone set.
The operation of the conventional radio button telephone equipment having the above construction will now be explained. First, the explanation will be made of the operation in the case where signal transmission is made from the child telephone set 7. It is confirmed by the line condition display lamp 8 that a line connected to the public telephone interface section 6 is vacant. After the vacant line has been seized, the operation button 9 is depressed to make signal transmission. In this case, the line condition display lamp 8 shows that the child telephone set 7 itself is in use. Next, explanation will be made of the operation in the case where the child telephone set 7 answers to call incoming. When a signal representing call incoming is detected by the bell detector 2, the child telephone set 7 displays an "under call incoming" condition by the line condition display lamp 8 to operate a ringer. If the operation button 9 is depressed in this state, the child telephone set 7 answers to the call incoming so that conversation becomes possible and the line condition display lamp 8 is changed into a state of display of an "under conversation" condition.
In the above-mentioned conventional radio button telephone equipment, however, only the condition of the line connected to the parent telephone set is displayed by the line condition display lamp of the child telephone set. Therefore, in the case where the parent telephone set is connected as an extension telephone terminal to an extension telephone port of a private automatic branch exchange, the conventional radio button telephone equipment provides a problem that the equipment is different in operability and available service function from a button telephone set connected to the private automatic branch exchange. Namely, it is not possible to know the use condition of a public telephone line connected to the private automatic branch exchange even if signal transmission is desired for the public telephone line. Also, a public telephone line held by the private automatic branch exchange cannot be released from the hold. Further, the transfer to an extension telephone set of the private automatic branch exchange is not possible. Accordingly, in order to use the radio button telephone equipment as an extension telephone set of the private automatic branch exchange, there is no means other than the reconstruction of the private automatic branch exchange itself or the replacement of the private automatic branch exchange by one which is capable of coping with the requirement.